Patent GB-774485-A (GB)
Title: Improvements in or relating to discharge apparatus for reproducing electrical signals
IPC: G11B11/10
Filed: 1953-03-16
Abstract: 774,485. Cathode ray tubes. ARMOUR RESEARCH FOUNDATION OF ILLINOIS INSTITUTE OF TECHNOLOGY. March 16, 1953 [April 11, 1952], No. 7170/53. Class 39(1). [Also in Group XL(b)] A cathode ray tube comprises means for deflecting a primary electron beam over a target associated with a moving magnetic tape having transverse lines of megretiration representing a record signal, the primary beam or secondary electrons generated thereby at the target being deflected by the magnetic fields of the tape over one or more output electrodes so as to vary the number of primary or secondary electrons collected thereby so as to generate an output signal representing the information recorded on the magnetic tape. In the reproducing head a ribbon beam is swept by coils over the tube end wall 208, Fig. 4, and a magnetic tape 210 of plastic or paper with a coating of magnetic material is fed continuously past the end wall 208. The tape carries a video signal and preferably also an andio signal at one edge thereof, the anotio head 213a being preferably disposed within the tube end wall, as shown. A row of about 500 wires 214 of high permeability material are embedded in the tube end wall; they may be of an alloy of 47-50 per cent. Ni and the remainder iron except for 0À05 per cent. C, 0À6 per cent. Mn, 0À01 per cent. P, 0À25 per cent. Si, 0À02 per cent. S which has a matching coefficient of expansion with the glass. The tape sets up magnetic fields between the wires so as to deflect the beam at right angles to the row of wires, and collector plates on either side of the row receive the deflected beam. Baffle plates close to the target system limit the width of the ribbon beam, and the output is delivered to a push pull circuit. Alternatively there may be only one collector plate feeding a "single ended" amplifier. In another embodiment, Fig. 5, the ribbon beam is positioned by plates 237, 238 and swept by plates 243 to pass through slit 234 in baffle plate 236 and is then deflected downwardly by plates 241, 242 or by magnetic means, the magnetic field of the tape 245 being applied by means of grid 247 to deflect the beam over targets 239, 240. The latter grid comprises a row of wires of high permeability material sealed through the tube wall at one end and connected by a support and terminal bar at their other ends (inside the tube), Figs. 6, 7 (not shown). There may be only one target. In another embodiment, Fig. 8, the magnetised tape deflects secondary electrons emitted by target 277 over collector 284 when primary beam 269 is swept over it. Target 277 comprises a beryllium copper strip having coatings of silver oxide and of caesium, or a beryllium strip alone. The beam is kept accurately on the target by baffle plates as in Fig. 17 (not shown) or by automatic control of the deflection voltages 283 accelerates and focuses the secondary electrons and is so shaped as to give a linear relationship between the magnetic fields of the record member 272 and the proportion of electrons received by the collector. Collector 284 may be replaced by an electron multiplier. Specifications 774,486 and 774,487 [Group XL(b)] are referred to.